[cfe-dev] RFC: allowing EH constructs, but not generating handlers/cleanups

[Hubert Tong via cfe-dev]

On Wed, Mar 22, 2017 at 7:21 PM, Hal Finkel <hfinkel at anl.gov> wrote:

>
> On 03/22/2017 06:17 PM, Hubert Tong via cfe-dev wrote:
>
> -fno-exceptions causes EH constructs such as try/catch,
> function-try-blocks, and throw expressions to be diagnosed with a severe
> error. That is, -f[no-]exceptions controls a language-support property.
>
> For experiments in evaluating the cost of (unused) exception handling, and
> for cases where components are being deployed with the expectation that
> exceptions will not be thrown, etc. it is useful to allow EH constructs in
> the source, but to generate code with no handlers or cleanups.
>
> I think that it still makes sense under such a mode to allow throw
> expressions to throw. This is consistent with -fno-exceptions still calling
> __cxa_bad_cast and __cxa_bad_typeid (which GCC also does, but not with
> __cxa_throw_bad_array_new_length).
>
> That is, the proposed semantics is essentially the same as for
> -fno-exceptions, except to treat try/catch and function-try-blocks as just
> normal code introducing no handlers, and to allow throw expressions.
>
> -fno-exceptions already suppresses creation of cleanups for unwinding and
> the ignoring of exception specifications.
>
> I like to think of this as -fignore-exceptions. I have a use for this, and
> I would like to know what people think.
>
>
> To summarize, code compiled with -fignore-exceptions can throw, but can't
> catch anything. All exceptions just unwind through all such code. Is that
> right?
>
That depends on what you mean by "unwind". Exceptions will go past all such
code without executing destructors.


>
>  -Hal
>
>
> -- HT
>
>
>
> _______________________________________________
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>
> --
> Hal Finkel
> Lead, Compiler Technology and Programming Languages
> Leadership Computing Facility
> Argonne National Laboratory
>
>
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